Resonant line



Patented Dec. 5, 1939 UNITED STATES PATENT OFFICE RESONANT LINE Nils; E. Linrlenblatl,r Port Jefferson, N. Y., assignor to RadioV Corporation of America, a corpoknown as resonant lines. Such lines .i usually comprise apair of coupled concentric conductors which are employed for controlling the frequency of an electron discharge device oscillation generator, or wherever there is need for a parallel tuned circuit. Reference isherein made to the article by Clarence W. I-Iansell, entitled Resonant lines for frequency control, published in Electrical Engineering for August, 1935, pages 852-856, and

to the article by Clarence W.A Hansel] and Philip S. Carter entitled Frequency control by low power factor line circuits, published in the Proceedings of the Institute of Radio Engineers,

April, 1936, pages 957-619, and to United States Patents Nos. 2,077,800 and 2,108,895, granted April 20, 1937 and February 22, 1938, respectively,

to Fred I-I. Kroger, for a more detailed description of the electrical properties and characteristics of these lines. i

Heretofore, it has generally been the practice touse the resonant concentric line only with the extremely high frequencies, due mainly to the fact that the line has appreciable length'and occupies much desirable space. Such lines, in many instances, may have a length approximately equal to one-quarterof the physical length of the operating wave. It will thus be seen that at a working wavelength of nine meters, for example, the

length of the resonant line at a quarter wavelength is about seven feet.v For relatively lower frequencies, however, the line becomes correspondingly longer and more cumbersome.

The present invention is designed to overcome the disadvantages of using long resonant lines and provides shortened line resonator which is compact and occupies little space. It is thus possible to use the shortened resonant line of ythe invention at lower frequencies than heretofore deemed practical previous types of resonant lines.

In brief, the shortened resonant line of the invention comprises a line which is folded concentrically instead of continuing in a straight line, as heretofore. A more detailed description of the invention follows in conjunction with the drawing wherein Figs. 1 and 2 illustrate two different embodiments of folded resonant lines in ,5,0 accordance'with the invention.

Referring to Fig. l in more detail, there is shown a resonant line comprising an outer cylindrical conductor i8, an inner conductor I4 at-the center, and intermediate cylindrical conductors II, I2 and I3. Cylindrical conductors I I andI I 3 1937, Serial No. '118,971

(el. irs-44) are connected to one base I5 of the line and conductors I 2 and I 4 are connected to the base I6 of the line to form folds, for simulating a continuous line. To obtain a uniform line effect, that is, substantially uniformly distributed inductance and capacity throughout the folded line, the diametrical ratios of the folded'sections of the lineas measured fromthe longitudinal axis ofthe line, are made to be the same. In other `words, the ratio of the diametrical distances b is made equal to the ratio of the distances .E d n and to equal the ratio of the distances or l ib d f The diametrical distance bl differs from c by the thickness of thelmaterial of the cylindrical wall I I and similarly d differs from e by the thickness ol the material of the cylindrical wall I2. If desired, the uniform line effect may be departed from and a concentrated or lumped reactance effect obtained by changing the diametrical ratios, especially if it is desired to still further reduce the total length of theA resonant line. A decreased diametrical ratiowill give an increased capacity per unit length of line. In this manner the folding up feature may be combined with the provision of a lumped capacity, and where this is elfected, it is preferred thatvit be done at the free end of the line, i. e., at the last sectionfwhere the diametrical ratio between inner conductor I4 and cylindrical wall I3 may be made smaller than the ratios betweenv the other adjacent concentric surfaces. Thus, there can be obtained two degrees o-f freedom or two tuning points, a mode of operation seldom desired, except in filter circuits.

In the line of Fig. l, the current is largest at the base of the line I 5 where the incoming feeder I7 is connected to the cylindrical wall Il. Consequently, it is at this point that there is provided the largest cross section in order to give the smallest resistance effect. Since the high voltage point is developed between the innermost conductor I4 and its vadjacent cylindrical conductor I3, and the spacing therebetween is the smallest, the precaution must.A be observed that the voltage gradient between these conductors be not too high. For certain spacings between the innermost conductor I4 and its adjacent conductor I3, there will be found to be certain limiting voltage values. v

Where concentrated reactance (lumped capacity) efects are not present, such as may be due to a diiference in diametrical ratios of the conductors, as mentioned above, it is preferred that the total length of the folded concentric resonant line of Fig. 1 be approximately onequarter the length of the communication wave; that is, the sum of the lengths of conductors II, I2, I3 'and lli, as measured from their respective bases I5 or I6 to which theyare. connected to their open ends, should be approximately onequarter the length of the operating wave.

The resonant line of Fig. 1 is herein shown as a frequency control line for the electron-discharge V device vacuum tube oscillator circuit connected to lead I1. This external circuit, however, is merely given for the purpose of illustration and is not to be construedas being limitative of the invention since the line may be used in other capacities, and other modes of coupling thereto may be provided. For example, instead of the direct coupling over lead I1 we may provide capacitive coupling to the line at points of higher voltage, of which the free end of each fold is the extreme. Two such methods of capacitive coupling comprise condenser I8 and conductor I9, shown in dotted lines connected to the free end of inner conductor IA, and condenser 2'and lead ,ZI shown. in dotted lines connected to the free end of conductor I3. Similarly, where desired, magnetic coupling may be employed, such as shown by dotted loops 22 and 23 which are connected near the outside of and close to the base of a fold where there is a large or relatively strong magnetic field. Thus, for example, where conductors I0 and I I make one fold, the loop 23 is located,y

correctly nearest the smaller conducto-r I I and at the base of the fold. It is preferred that the magnetic coupling obtained by loops 22 and 23 be nearest the greatest ow of current withinl each space for each section in order to obtain close coupling. This effect of close coupling is greatest at the place where the iield gradient is greatest, and such a location will be near the smallest diameter wall of each section. A looser magnetic coupling` may, of course, be obtained by coupling a loop at places other than that shown by loops 22 and 23, such as at`24. It will thus be seen that i there may be provided eitherconductive, capacitive, or magnetic coupling, and various degrees of coupling. These methods of coupling enable the line to `be used for many purposes, not only as a frequencycontrol line for an oscillator, but also as a combined tank circuit and coupling unit between'` stages. For example, if it is desiredY to employ the resonant line of Fig. 1 as a coupling circuit between stages, loop 22 canbe connected to the output of one stage, and loop 23 connected to the input of the succeeding stage.

The larrows in Fig. 1 of the drawing indicate the direction of thefiow of current, and it will be seen that the shell current 'in one section becomes the center conductor current in the next section. Fig. 2 shows an alternative folded resonant line in accordance with the invention, where the next just the opposite shown in Fig. 1.

of what is found in the une t We thus have, in Fig. 2, a high voltage end at the largest diameter section and a high current end at the smallest diameter scc- `tion. The external circuit may be coupled either `conductively, magnetically, or capacitively to the resonant line of Fig. 2 in a manner somewhat similar to that shown in Fig. 1; that is, the capacitive coupling may be effected at points of high voltage, whereas the magnetic coupling may 1 be eiected at points of greatest current flow.

VIt will be understood, ofr course, that the ininvention may be tapered to give the same constant ratio between the center and the shell of the conductors as mentioned above in connection withv Fig. 1; The larger diameters canthen be used as a high current end of the line. In this case, of course, the amount of taper will naturally be limited by the corona limit at the high voltage end in the event that extremely high voltages are used. v

What is claimed is: y

1. A folded, resonant line comprising an outer'-v yconductor and a` concentric central conductor electrically coupled together at one end, and an intermediate concentric conductor constructedv and arranged to be electrically coupled to said 3 outerconductor at its other end, said intermedi.-

ate conductor extending substantially parallel to said central conductor for the greater portions o-f thel lengths of the last two conductors, the sum of the lengths of said central and intermediate conductors having a predetermined relation to the wavelength of oscillation of said resonant line.

'2. Afolded, concentric resonant line comprising an outer cylindrical conductorand'a central conductor, a mechanical and electrical connection between said conductors at one of theiradjacent ends, and an intermediate cylindrical conductor constructed and arranged to be mechanically and electrically coupled to the other end of said outer conductor, said intermediate conductor extending parallel to said central conductor for the greater portions of the lengths of the last two conductors, the sum of the lengths of said central and intermediate conductors having a predetermined relation to the wavelength of oscillation4 of said resonant line.

'3. A folded, concentric resonant line comprising an outer conductor, an inner central conductor, and a plurality of intermediate concentric conductors parallel and surrounding the greater part of the length of said central conductor, adjacent ones of said intermediate conductors being so constructed and arranged as to be conductively connected at one of their respective ends Yto opposite ends of said outer conductor, the other ends of said intermediate conductors being free, alternately located ones of said conductors withinsaidl outer conductor being connected to the same end of said outer conductor.

4. A resonant line in accordance with claim 3 characterized iny this that said outer and inner conductors are cylindrical.

5. A folded, concentric resonant line comprisingan outer conductor, an inner central conductor, and a plurality of intermediate concentric conductors located within said outer conductor and between said outer conductor and said central conductor, adjacent o-nes of all of said inner conductors being connected at one of their respective ends to opposite ends of said outer conductor, the other ends of said inner conductors being free, alternately located ones of said inner conductors being connected to the same end of said outer conductor, said intermediate conductors being so arranged that the diametrical ratio measured from the longitudinal axis of said resonant line to any two adjacent surfaces of adjacent conductors is the same throughout said line.

6. In combination, a resonant line Acomprising an outer conductor and a concentric central conductor electrically coupled together at one end, an intermediate concentric conductor constructed and arranged to be electrically coupled to said outer conductor at its other end, and a utilization circuit conductively coupled to said intermediate .conductor in the interior of said resonant line at a location where there is substantially the greatest flow of current in said line.

7. In combination, a folded, concentric, rescnant line comprising an outer cylindrical conductor and a central conductor, a mechanical an'. electrical connection between said conductors ai one of their adjacent ends, an intermediate cylin drical conductor constructed and arranged to be mechanically and electrically coupled to the other end of said outer conductor, and a utilization cir cuit conductively coupled to a point of low potential on said line.

8. In combination, a resonant line comprising an outer conductor and a concentric central conductor electrically coupled together at one end, an intermediate, inner, concentric conductor electrically coupled to said outer conductor at its other end, and a utilization circuit conductively coupled to said intermediate conductor at a location near the junction of said intermediate conductor with said outer conductor, the sum of the lengths of said inner conductors being approximately one-quarter of the length of the wave to whose frequency the line is resonant.

9. A folded, concentric resonant line comprisving an outer conductor, an inner central conductor, and a plurality of intermediate, inner, concentric conductors, adjacent ones of said inner conductors being connected at one of their respective ends to opposite ends of said outer conductor, the other ends of said inner conductors Y being free, alternately located ones of said innerA conductors being connected to the same end of said outer conductor, the sum of the lengths of all of said inner conductors being approximately one-quarter of the length of the wave to whose frequency the line is resonant.

10. In combination, a resonant line comprising an outer conductor and a concentric central conductor electrically coupled together at one end, an intermediate inner concentric conductor electrically coupled to said outer conductor at its other end, the sum of the lengths of all of said inner conductors being approximately one-quarter of the length of the Wave to whose frequency the line is resonant.

11. A folded resonantline comprising an outer yconductor and a concentric central conductor to one of said first two conductors at its other end, said intermediate conductor being so constructed and arranged that the diametrical ratio measured from the longitudinal axis of said line to any two adjacent surfaces 0f adjacent conductors is the same throughout said line.

13. A compact concentric resonant line comprising an outer cylindrical conductor and a centrol conductor, a mechanical and electrical connection between said conductors at one of their adjacent ends, an intermediate cylindrical conductor constructed and arranged to be mechanically and electrically coupled to the other end of said outer conductor, the sum of the lengths of said central and intermediate conductors being related to the Wavelength of oscillation of said resonant line. 

